Acidic tin depositing bath



United States Patent 6505921 U5. (:1. 2o4-s4 rm. c1. C23b 5/14, 5/46 2 Claims The invention relates to an acidic tin-depositing bath on the basis of sulphate, sulphonate or fiuoborate by means of which bright tin deposits can be obtained.

Such baths are known, it is true, but a bath suitable for continuous operation has not yet become available. A makeshift was sometimes a tin deposit obtained with a dull surface, which was subsequently rendered bright by superficial heating just above melting point. However, this is a particularly circuitous method and the aftertreatment is very critical in view of temperature and duration of heating.

A type of known bright tin-depositing baths contains as a brightening agent, a combination of two colloids of opposite electrical charges, for example a phenol resin and an extract of beech wood. However, these baths are very unstable, so that they are not suitable for practical use. Moreover, this type of brightening agent contaminates the work pieces to a high extent so that an additional cleaning operation is required after the work piece is removed from the bath.

There are moreover known acidic tin-depositing baths containing as a brightening agent a condensation product of an aliphatic aldehyde and an organic compound containing an alkaline, nitrogen-containing group, for example, a reaction product of acetaldehyde and otoluidine. However, these brightening agents become very soon resinous, so that the bath possesses only a very short life.

Finally acidic tin-depositing baths are known containing 'as a brightening agent an aromatic or heterocyclic aldehyde and, in addition, formaldehyde. A disadvantage of these baths is, however, that they provide bright deposits only in a very narrow range of current densities, i.e. between 5 and a./dm. This means that strongly profiled work pieces having sharp edges and small apertures, the deposition of tin on which gives rise to current density variations by a factor of even 100, cannot be covered with a uniform tin deposit of uniform gloss. The current density variations are even much larger in the case of tin deposition with the aid of drums.

The tin-depositing baths according to the invention permit of obtaining without difficulty bright tin deposits, even on sharply profiled work pieces having sharp edges or small apertures and even in an electroplating process by means of a drum. In operation this bath allows variations in current density up to a factor 1000 without any objection. Moreover, the tinplating baths according to the invention are extremely stable.

The acidic electroplating bath containing bivalent tin ions and, as anions, sulphate-, sulphonateor fluoborateions is characterized in accordance with the invention in that it contains as a brightening agent one or more adequately soluble compounds of the general formula:

RrCC-Rz II II 0 wherein R is an aliphatic, aromatic, alicyclic, or heterocyclic group or a mixed aliphatic-aromatic group having, as the case may be, nonionisable substitutes or substituents not reducible in this medium, and R is hydrogen or one of the said groups or wherein the group:

RrC-C|3-R2 t t is a ring system or part of a ring system and in that, moreover, the bath contains a surface-active compound of non-ionic character.

It should be noted that the addition of non-ionic, surface-active substances as grain refiners is known. In accordance with the applicants experience these additions do not impart gloss to the tin deposited from said baths.

From the investigations leading to the present invention it appeared that the effect of the brightening agent gets lost, if the aforesaid compound contains a substituent reducible in this medium, for example a nitro-group or an ionisable substituent, for example a sulphonic acid-, a carboxylic acid-, an aminoor a substituted amino-group. Derivatives of ketones or keto-aldehydes operating as brightening agents in the scope of the invention, for example coupling products with aniline, so-called Schifis bases, have the same effect, since, dissolved in the tinplating bath, they are converted by hydrolysis into the ketones or keto-aldehydes themselves.

Whereas in the known baths, to which a compound containing a carbonyl group is added as a brightening agent, the presence of formaldehyde or acetaldehyde is necessary, in order to obtain the desired gloss of the tin deposit, these substances must be absent in the electroplating bath according to the invention in order to obtain a bright deposit.

The quantity of the brightening agent to be added for having a satisfactory brightening effect need only be small: quantities from 25 to 500 mg. per liter of bath liquid are in a satisfactory way active. There is no limit above which the effect disappears, but the addition of large quantities is, of course, not advisable for economic reasons. Moreover, a limit may be imposed by the solubility.

EXAMPLES As a basic bath an aqueous tin-plating bath of the following composition per liter of liquid was used G. Stannous sulphate 40 Sulphuric acid (d=l.84) Lissapol N 1 Lissapol N is a non-ionic, surface-active substance, a condensate of alkylphenols and ethylene oxide.

To this bath one of the following brightening agents was added in quantities varying between 25 and 500 mg. per liter of bath liquid. The tin-plating baths thus obtained were used at a temperature of 20 C. for tinplating strongly profiled work pieces in an electroplating drum device. The average current density was between 0.5 and 5 'a./ dm. The baths had the same efiect for weeks without soiling.

The brightening agents employed are:

II II B I'HnC-C-C-CHaBt 1,4-d1bromobutane-dtone-2,3

Hexane dione 3,4

C-CCHa Phenyl-methyl-glyoxal Benztl C-CH Phenylglyoxal Cyclohexane-dtone 1,2

Dlphenyl-trlketone A similar result was obtained with the aid of a tinplating bath of one of the following two compositions, to which one of the afore-said brightening agents was added. 5

Tin fiuoborate Sn(BF g Fluoboric acid HBF g 200 60% solution of Lissapol N ..-I n1-- 2 30 Tin sulphate g m-Benzene disulphonic acid g 170 solution of Lissapol N ml 1 35 What is claimed is:

1. An aqueous acidic electro-plating bath for depositing tin, containing bivalent tin ions, as anions sulphate-, sulphonateor fluoborate-ions and, as a brightening agent, one or more sufiiciently soluble compounds of the general formula:

Rr-fi-C-Rl 0 0 wherein R is an aliphatic, aromatic, ,alicyclic or heterocylic group or a mixed aliphatic aromatic group, substituted only with non-ionisable substituents or substituents not reducible in said bath and R is hydrogen or one of the said groups or wherein the group References Cited UNITED STATES PATENTS 1/ 1949 Du Rose et a1 204-43 1/ 1968 Korpiun et al 204--54 JOHN H. MACK, Primary Examiner.

G. KAPLAN, Assistant Examiner. 

1. AN AQUEOUS ACIDIC ELECTRO-PLATING BATH FOR DEPOSITING TIN, CONTAINING BIVALENT TIN IONS, AS ANIONS SULPHATE-, SULPHONATE- OR FLUOBORATE-IONS AND, AS A BRIGHTENING AGENT, ONE OR MORE SUFFICIENTLY SOLUBLE COMPOUNDS OF THE GENERAL FORMULA: 